Change signature of lookupConstructor to only require a name.

pkg/compiler/lib/src/ssa/builder.dart

Index: pkg/compiler/lib/src/ssa/builder.dart
diff --git a/pkg/compiler/lib/src/ssa/builder.dart b/pkg/compiler/lib/src/ssa/builder.dart
index 239aea90b9eca8ad971c26caa358a7d947fce129..ac2b436c19a040a0bddd986076ccdd8be657a523 100644
--- a/pkg/compiler/lib/src/ssa/builder.dart
+++ b/pkg/compiler/lib/src/ssa/builder.dart
@@ -1878,14 +1878,14 @@ class SsaBuilder extends ResolvedVisitor {
       if (!enclosingClass.isObject) {
         assert(superClass != null);
         assert(superClass.resolutionState == STATE_DONE);
-        Selector selector =
-            new Selector.callDefaultConstructor(enclosingClass.library);
         // TODO(johnniwinther): Should we find injected constructors as well?
-        FunctionElement target = superClass.lookupConstructor(selector);
+        FunctionElement target = superClass.lookupDefaultConstructor();
         if (target == null) {
           compiler.internalError(superClass,
               "No default constructor available.");
         }
+        Selector selector =
+                    new Selector.callDefaultConstructor(enclosingClass.library);
         List<HInstruction> arguments =
             selector.makeArgumentsList2(const Link<ast.Node>(),
                                         target.implementation,